Metal Catalysed Cross-Coupling Reactions of Heterocycles

Abstract

This report describes two methodology studies dedicated towards development of metal catalysed crosscoupling reactions in the synthesis of novel heterocyclic compounds.

Firstly, a Heck-Mizoroki arylation reaction is reported for the direct functionalisation of tetrahydropyridines, towards the synthesis of kainoid analogues. Kainoids are a group of non-proteinogenic pyrrolidine dicarboxylic acids, which have attracted considerable interest because of their potent biological activity, including insecticidal, anthelmintic and neuroexcitatory properties. The ideal synthesis of kainoids would allow the ability to introduce various side chains at the C-4 position to access diverse pharmacologically active kainoid analogues. Tandem asymmetric Heck-Mizoroki arylation reaction and [2,3]-sigmatropic rearrangement provides a quick and efficient way to access these molecules. The Heck-Mizoroki arylation of 1-methyl-1,2,5,6-tetrahydropyridine and its hydrochloride salt is reported, with the arylation in the 3- position of the tetrahydropyridine as the major product. The reaction has been applied to a variety of substituted aryliodides, with promising results, demonstrating functional group tolerance of the method, however isolation and purification of the resulting compounds has remained challengeing. Diarylation of tetrahydropyridines has also been achieved.

Secondly, a new catalytic method for arylative spirocyclisation is reported, using stoichiometric Grignard reagents and iron(III) catalysts, to induce cyclisation of (2-iodo benzyl ethers of furan in a highly stereoselective manner to produce novel functionalised spirocyclic compounds. Method optimisation and application of a variety of Grignard reagents is reported with aryl cross-coupling achieved in high yields. Alkyl- cross coupling has also been achieved with ethylmagnesium bromide Grignard reagent.